Flask-shaped containers are conventionally employed in some liquid product applications, such as liquor. Such flask-shaped containers have opposed relatively closely spaced front and back walls, and opposed relatively widely spaced sidewalls that interconnect the side edges of the front and back walls. Vacuum assistance is conventionally employed to increase the filling speed of liquid into containers, including flasks. Such vacuum-assisted filling involves withdrawal of air from the container interior while simultaneously injecting liquid into the interior. Vacuum-assisted filling typically does not present a problem with flask-shaped containers of glass construction, for example, because the container walls are sufficiently rigid to withstand the internal vacuum forces during and after the filling operation. However, vacuum-assisted filling can present problems with flask-shaped containers of molded plastic construction because the large front and back walls of the container can deform inwardly under the internal vacuum forces. That is, internal vacuum pressure on the relatively large front and back walls of the container tend to distort these walls inwardly. A major portion of at least the front wall, and typically both the front and back walls, of flask-shaped containers is conventionally occupied by a panel area to which a label is affixed. In some containers, particularly of molded plastic construction, ribs or bumpers are provided at the opposed upper and lower ends of the label panel area(s) to protect the label during handling of the container. These bumpers are conventionally of either uniform radial depth with respect to the adjacent label panel area, or decrease in depth toward the sidewalls of the container so as to blend into the label panel area at the sidewalls. It is a general object of the present invention to provide a flask-shaped container of molded plastic construction that has improved vacuum resistance to reduce distortion of the label panel area(s) during and after filling, and which facilitates automated handling of the containers during the fabrication and filling processes.
A flask of molded plastic construction in accordance with one exemplary but presently preferred aspect of the invention includes opposed front and back walls, at least one of which has a convex label panel area at a first radius of curvature and a pair of spaced bumpers at opposite ends of the label panel area. The bumpers have a second radius of curvature that is greater than the first radius of curvature such that the bumpers have a radial depth perpendicular to the label panel area which is greatest at the ends of the bumpers and decreases toward the center of the label panel area. This bumper contour not only increases vacuum resistance to reduce distortion of the panel area due to vacuum filling, but also improves automated handling of the containers by reducing the tendency of the container sides to overlap or “shingle” during automated handling.
A dual convex flask in accordance with an exemplary presently preferred embodiment of the invention is of one-piece integrally molded plastic construction. The flask has opposed front and back walls, and opposed substantially flat sidewalls that connect adjacent side edges of the front and back walls. The front and back walls each have a convex label panel area at a first radius of curvature and axially spaced bumpers that extend outwardly from opposite ends of the panel area. The bumpers on each of the front and back walls have a second radius of curvature that is greater than the label panel area first radius of curvature, such that the bumpers have a radial depth perpendicular to the associated label panel area which is greatest at the ends of the bumpers adjacent to the sidewalls and least at the center of the panel area.